<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var year = prompt("请输入您出生的年份")
        var age = 2020 - year
        alert(`您今年${age}岁了`)
    </script>
</body>
</html>